Light and Easy Water Filtration for the Lazy Backpacker
on 08/09/2007 13:27:32 MDT

Over the years I’ve spent backpacking through the nearby Uwharries and Appalachian Mountains I’ve used a number of methods to insure the purity of my drinking water. A couple of things I have decided. First I don’t like chemicals. Sure they are lightweight but I don’t like the taste. Why in this world would anyone hike to a clear running mountain stream and add chlorine to it? It just ruins the taste. And have you read the wait times on the label? I’m just too impatient to wait thirty minutes to kill what may (or may not) be lurking in my next thirst quenching drink. By the way that does not include the four hours for cryptosporidia.

As for water filters I have problems with them as well. After a long hike who wants to spend time hand pumping water? Certainly not me. All I want to do is drink the water. As for weight the lighter the pump the more pumping is required. Until recently I carried a Kaytadyn Hiker. It delivers about 1 liter a minute. Their new lighter weight model only supplies a ½ liter a minute to safe a whole 3 ounces. That’s a lot of pumping when you are hot and tired and just need to relax.

A few weeks ago I came across a possible solution. Kaytadyn markets a gravity filter. A Hiker filter cartridge is mounted in a dry sack. Water is collected in the sack and filtered water is deliverer by a tube for drinking. However just as I was about to order one to try on my next trip I spotted a drawback. It weighs 15.5 ounces. But I did like the concept. I started playing around with some materials and came up with a homemade version that weighs about 8 ounces. While it is still heavier than chemicals it is as light as their lightest filter. I decided to try it out on a week-long trip in the Smokies. Not only did it perform well, it supplied three hikers with all the water we wanted the entire week. The best part is while others were pumping or adding chemicals we were setting back enjoying the scenery and cool mountain water. We were also the object of a lot of attention with questions about our water filter system.

So here is how to make a gravity filter from readily available parts. First the materials.

The mouth of the Nalgene bottle is a perfect fit for the filter cartridge. I also added a quick connect adapter to the tubing to attach to my hydration bladder. CamelBak markets a set for $7.00.

Putting this together is really easy. If you can handle a utility knife without cutting yourself you have all the skills you need. Start by cutting the water bottle below the plastic ring at the screw threads. Make the cuts as smooth as possible to avoid damaging the bag over time. You can smooth this even more with a piece of sandpaper I’ll refer to this part as the bottle neck.

The next step is to cut the water bottle cap to allow the filter to fit through. All that is really needed are the screw threads so don’t be afraid to cut. Use medium grit sandpaper to smooth the inside of the cap ring and to insure the filter cartridge will pass through the cap.

Screw the cap ring onto the water bottle neck and check if the filter cartridge will slide in. The fit should be tight. Once you have the hole the correct size, place the bottle neck inside the water bag with the threads centered on the bottom of the sack. The position is not critical. Now screw the cap ring on the bottle neck over the bag from the outside.

Cut away the cloth inside the ring. Some cloth around the edge may be left.

Now spread a small amount of the lubricant that came with the filter around the black O-ring. Slide the filter through the bottom of the bag so that the discharge is on the outside of the bag. Attach the tubing to the filter and fill the bag with water. You will have to prime the filter the first time you use it. Be careful not to suck the carbon into you mouth. It will not hurt you but it’s not a pleasant experience. Allow at least a liter of water to pass through the filter prior to the first use.

As I mentioned earlier I connect the filter to my water bladder to refill it. The higher the filter is above the bladder the faster it will fill. The time to fill the 70 ounce bladder varies but usually it is full in 2-3 minutes. Of course since I’m not pumping I really don’t care if it fills at a rate of less than one liter a minute.

Maintenance on the filter is easy. If the filter clogs in the field, Kaytadyn has a pre-filter sleeve on the cartridge that can be removed and cleaned. Since this is on the pre-filtered side it can be cleaned in untreated water. The filter cartridge itself can be rinsed in untreated water to help clean it. Just keep the discharge opening covered to prevent contamination. Kaytadyn claims about 200 gallons from one filter depending on the water. I never got that much from a pump but without the pressure of the pump I am hoping to come close.

After a trip I remove the cartridge from the bag and wash the bag with clean water. The tubing and cartridge are washed in a 10% bleach solution and allowed to sit in the mixture about 30 minutes. I figure that should kill most anything trapped in the filter. I then allow it to dry over-night prior to storage. Before I use the filter on the next trip I run about a liter of water through the unit to flush out the taste of bleach. This is the same procedure I used for several years with the Hiker pump.

While hiking I keep the hose in a snack size zip lock bag. This helps avoid any contamination. I use the smallest stuff sack that came in the set of three to hold the filter/bag, cleaning sponge and baggy with tubing. It is stored in the top of my pack so I can get to it easily.

After I built mine I discovered you can buy a similar filter from ULA. It’s called the Amigo Pro. With shipping it cost about the same, but if you have an old Nalgene laying around and a spare silnylon sack, build your own.

Light and Easy Water Filtration for the Lazy Backpacker
on 08/09/2007 14:45:56 MDT

Cross contamination is not really a problem during fitration. It is only during storage since the hose and water bag are stored together. By placing the hose in a snack size baggie this should prevent the problem.

I really don't worry about it too much since I am very picky about my water source. An article earlier this year titled Sipping the Waters: Techniques for Selecting Untreated Backcountry Water for Drinkingby Michael von Gortler, MD is a great guide to choosing water sources. I pretty much follow the suggestions and still filter to stay on the safe side. There have been a few sources I have decided to trust but it was water running out of cracks in rocks where there were no obvious signs of large mammals.

Light and Easy Water Filtration for the Lazy Backpacker
on 08/10/2007 05:50:14 MDT

After attaching the hose to the filter I dip the bag into the water source. Just keep the hose out of the water as much as possible. I usually hold the end of the hose up with the top of the bag and that way water does not start to flow until I have hung the bag.

Light and Easy Water Filtration for the Lazy Backpacker
on 08/10/2007 05:53:15 MDT

I dip the open end of the bag into the water source while holding the hose out of the water. As long as the discharge end of the hose stays above the water level no water passes through the filter. If you connect the top of the bag you can use it as a handle to carry water back to where you are camping/cooking. Then connect to your water bottle or bladder and shortly you will have cool clean water to drink.

your setup looks really nice. I had played with the same idea of a dry bag but desided to go with the ray way or ULA style.

The one pictured below weighs in at 6oz and I use my bear bag line to hang it. To save even more weight I've used the hose from my blader As Bill does but I don't always have it in the summer. I've found this setup works well.

I did some searching on this site and found Bills set up however no one had sourced the nylon fittings. I did some searching on the web and found them in a few places.

I use a Hiker Pro filter cartridge but it's been cut down quite a bit. all the threds and extra weight are cut off as I don't need them.

I'm not really a hudge weight guy as I could use to drop a few pounds over any of my gear. ;-)

I used the Cuben becasue I had it. My weight is with a wet filter as well. I weighed it right after i took it down.

The biggest savings for me was using the bear bag line to hang it, using the blader hose right to it, and cutting the filter down saved about an ounce. I could have dropped a few more if I didn't use the metal rings and made the over all pattern a bit smaller. I used 24" round but I thing bill and a few others have used 21"

Just FYI, Gardenville's project #3 from Sept 2005 on the following site does the same thing, modifying a ULA Amigo to use Cuben and cutting excess plastic off the filter itself:http://ultraliteskunkworks.blogspot.com/2005/09/cuben-connection.html

I have a ULA Amigo, and after I saw the above reference I cut off the excess plastic on mine too, using my bandsaw; pretty easy, saved a little weight, not a huge difference but somehow emotionally ... satisfying.

Light and Easy Water Filtration for the Lazy Backpacker
on 08/13/2007 05:22:39 MDT

The stuff sacks are in the camping (sports) department. All WalMarts do not have them. There are 3 store near my home and only one has them in stock. All three are Super WalMarts. Go figure!

As suggested by a few of the messages I cut away the threads on the filter (except for the last one needed to prevent it from pushing through the pastic ring on the bag). It lowered the weight about a 1/2 ounce.

Light and Easy Water Filtration for the Lazy Backpacker
on 08/13/2007 11:04:13 MDT

Joe

I only cut away at the end with the threads. If you look at one of the earlier messages it will show all the threads gone. I only cut to the last thread leaving a lip to stop the filter from going all the way through the mounting ring on the bag.

The setup the Amigo Pro and RayWay use puts the entire filter inside the bag so that none of the threads are needed. This is a good design just not the one I picked.